1. Field Of The Invention
This invention relates generally to a distance measuring system, and more particularly, to a distance measuring system for use on a golf course for enabling a golfer to accurately determine the distance between the current lie of his golf ball and the hole toward which he is presently advancing his golf ball.
2. Description Of The Prior Art
The prior art discloses various, relatively complex and expensive systems and methods for measuring distance. One such system is the Tellurometer system described briefly herein with respect to FIG. 4.
The Tellurometer system uses microwaves at about 3, 10, or 35 GHz as the carrier frequency. The measuring set consists of two active units with a transmitter and a receiver, one being called the master and the other being called the remote unit. The carrier frequencies of the two units differ slightly, making it possible to utilize intermediate frequency (IF) amplification. The microwave carriers are frequency modulated by measurement or pattern signals that are slightly different at the master and remote units, to create beat frequencies in those units. Also, several other nearby pattern frequencies build up the total unambiguous distance. The range of the modulation frequency varies according to the model between five and twenty-five MHz. Because the carriers are microwaves, the beamwidths are relatively narrow, usually between two degrees and twenty degrees. Measuring can be carried on either at night or daytime, through haze or light rain, although heavy rainfall may reduce the working range.
The bare outlines of the measurement principal are as follows: a frequency-modulated carrier wave from the master station is sent to the remote station, where it is received and retransmitted to the master station. There, the phase difference between the transmitted and the received modulation or pattern wave is compared. The distance can be determined by knowing the average velocity of the radio waves along the wave path and also the master modulation wavelength. The development of the Tellurometer system of measurements was initiated by W. Wadley in 1957 at The National Institute of Telecommunications Research of South Africa and is now the basis of all microwave distance measuring instruments.
None of the systems of the prior art relate in any way to measuring the distance between the lie of a golfer's ball and the hole toward which the golfer is presently advancing his golf ball.
All known distance measurement systems of the prior art are relatively complex, expensive, difficult to install and maintain, subject to many types of measurement errors, often occupy excessive bandwidths, are susceptible to noise interference, produce errors in the subcarrier filtering process, and/or require complex modulation/demodulation operations which can result in even more errors.
The present invention avoids all of these problems, while fulfilling a long-felt, and previously unfilled, need for a relatively simple, low-cost, easy-to-install and maintain system which uses a portable master transceiver station and at least one remote transceiver station.
The present system is far simpler than the Tellurometer system in at least two very significant ways. In the first place, the basic measurement frequency is the remote RF carrier frequency itself, for example, 318 MHz. Two separate and distinct phase measurements are made in rapid succession. One measurement is made with the master RF carrier displaced above the remote carrier frequency by an amount equal to the IF frequency, or approximately 248 KHz. The second measurement is made with the master carrier frequency displaced below the remote carrier frequency by the same amount. With these two phase measurements, range can be determined unambiguously over the required distance of at least three hundred yards, at least for golfing purposes.
Secondly, the phase information from the remote location is communicated to the master location by phase-locking the carriers together. This avoids the necessity of using modulated subcarriers to transmit this information. This, in turn, reduces the occupied bandwidth, greatly simplifies the modulation-demodulation required, and very substantially reduces errors otherwise introduced by the subcarrier filtering processes.